1. Field of the Invention
The present invention relates generally to the field of decal printing paper for ceramic surfaces. More specifically, the present invention discloses new decal printing paper designs, compositions and methods for transferring high resolution (up to 1200 by 1200 pixels per inch resolution) single- or multi-color images onto the matte, glossy, glazed or unglazed surface of inorganic (various forms of ceramic, porcelain, porcelain enamel, glass or metal) substrates and permanently affixing them to said substrate by heating in a kiln. The printing papers are useful in many of the currently available commercial laser printers that use inorganic toner formulations such as iron oxide, ceramic pigment and MICR toner.
2. Background of the Invention
Decals have been used for many years to transfer pre-printed designs to a substrate, such a ceramic object. A decal is typically a multi-layer construction with four layers as shown for example in FIG. 1. One layer is a base paper 10 that is the coated with a water-soluble release layer 12, often comprised of gum arabic. This two-layer paper is referred to as waterslide decal paper, waterslide paper, or just decal paper. It is widely used as the printing paper in digital decal printing devices and other printing methods such as screen printing for the production of waterside decals. Such waterslide decal papers are commercially available from a number of companies such a Tulliss-Russell Coaters.
Another layer 14 is the image transfer layer made of liquid ceramic cover coat. This material can be screen printed onto the decal paper or sprayed. This liquid material is commercially supplied by MZ Toner Technologies and others. Once the liquid layer dries, the paper is ready to be placed into a printer that prints the image 16. This image transfer layer material maintains the integrity of the printed image after the decal is immersed in water, releaser from the waterslide paper and transferred to the substrate being decorated.
An image transfer layer that includes additives in the coated transfer material has been developed and demonstrated by Zimmer in U.S. Pat. No. 6,068,692 to enhance the functionality and usefulness of printed ceramic decorations (decals). This approach is useful with laser printers using toners with inorganic materials such as ceramic pigments, iron oxide and MICR laser printer toner formulations. But this system requires that the image transfer layer must be applied to the decal in a secondary processing step that uses a thermal pouch laminator to bond the image transfer layer to the printed decal paper or liquid application via screen printing or aerosol spray.
Applying transfer material directly onto the waterslide paper and printing onto the image transfer layer directly by laser printing devices enables the one step production of a decal that is ready to use as a standard waterslide decoration. Papers of this basic design are commercially available but none of them include additives in the image transfer layer material that can enhance the performance and expand the usefulness of the one step printed decal.
The present applicant is unaware of any system of decal printing papers that encompasses all of the advantages of the present invention, including: (1) The ability to decorate a wide variety of substrates including those with matte, glossy, glazed and unglazed surfaces; (2) Single step printed decal production; (3) Food safety due to flux additives with low lead content in the transfer material; (4) Providing a means for identifying the functionalities of different image transfer materials by adding different dye colorants to the image transfer materials; (5) Expand the useful firing temperature range to as low as 1150° F. to achieve a wider color spectrum in the finished decoration; and (6) Additional background color or white background in the image transfer layer.
Several other methods for permanently affixing kiln-fired images onto ceramic surfaces have been patented (e.g., Geddes, U.S. Pat. No. 6,694,885 and Banhazl, U.S. Pat. No. 7,622,237 and others) but none use a simple one-step printed transfer paper that carries with it a glass frit/flux that expands the usefulness and performance of the paper as described in the present invention. The printed waterslide decal (transfer) papers described herein are unique in their ability to enable the expanded usefulness of decal decorations within a one-step, easy to use, inexpensive print and apply decal transfer print paper. In addition, the flexibility exists within the design of these transfer papers to print and apply either positive or inverted images to glossy, matte, glazed and unglazed surfaces to achieve a wide variety of decorating results and decal usefulness. Using this decal printing paper with a glass flux in the image transfer layer material, it is also possible to add secondary or tertiary film layers or other additives to further expand the functionality of the decals produced. Finally, the manufactures of the most widely used black-and-white laser printers that rely on an iron oxide black toner have begun to replace those toners with more industry standard organic printing toners that will not survive ceramic or glass firing temperatures in a kiln. This may render single-step papers without a glass flux in the image transfer layer, such as the Banhazl system, mostly obsolete.
Currently available single-step waterslide decal printing papers for producing decals with inorganic iron oxide printing toners carry no glass flux in the image transfer layer. For the inorganic material to adhere to the substrate, it must be applied on a glossy surface to be decorated and fired at temperatures high enough to soften the glaze or melt the iron oxide on the decorated surface. This is often higher than 1800° F. and may be as high as 2200° F. for some commercial items like ceramic floor tile. With the addition of a glass (frit) flux mixed into the image transfer layer material, we have demonstrated that this firing temperature can be reduced to as low as 1150° F. for a low melt point glass flux, and up to 1750° F. for a higher melt point flux in the image transfer layer material. Lower firing temperatures may be possible with the addition of a glass flux with a still lower melt point. This expanded (lower) firing temperature range improves energy efficiency by reducing the power consumption and duration of the firing process while still achieving sufficient image adhesion for the decorated item to be useful in commercial and artistic end uses on ceramic, glass and metal substrates.
In addition, heating the black iron oxide pigment (Fe3O4 magnetite) in the presence of oxygen converts the magnetite to hematite (Fe2O3) or more commonly known as rust. At the very high temperatures required by other one step papers, the black iron oxide pigment is fully converted to Fe2O3 and fully converts the black pigment into an orange or sepia pigment. Firing to the lower temperatures possible with these new papers preserves at least some of the original black color enabling the creation of a dark chocolate brown image. So, having flux additives in the image transfer material with specified melt points such as the ones used in these papers enables a range of colors in the fired decoration.
Furthermore, the addition of glass flux in the image transfer layer material expands the usefulness of these printing papers to enable decoration of artistic substrates that are matte or unglazed and no longer requires a glossy or glazed surface. Finally, incorporating an organic dye in the image transfer material allows the user to quickly differentiate the functionality of one paper from the others. No special equipment is needed and no exposure to hazardous materials is required. This firing temperature flexibility and economy has not been possible before in a one-step printed decal without the glass flux additive described herein. The efficiency of a one-step transfer of the printed image on a film layer that incorporates glass flux is novel. Additional functionality can result and have been demonstrated by using different types of glass flux, such as a low lead oxide glass that can result in a food safe decoration. Other types of additives may be useful, such as white or colored ceramic pigments, and are under development, to further expand the usefulness and design flexibility of the present one-step printed decal.
The present invention provides a set of decal printing papers that use a standard waterslide decal paper and are then coated with a transfer material that incorporates a glass flux. The addition of the glass flux in the transfer material expands the usefulness of this one-step printing paper design. This design of the decal printing paper enables a finished decal to be produced by direct printing in one step in any of a variety of commercial laser printers, in single color or four color. The flux in the image transfer layer enables a variety of performance advantages and enhancements beyond those that are currently available. Color coding the different papers with a color dye in the image transfer material simplifies the task of identifying which paper is most useful for a particular decorating objective.
The concept of printing an image transfer layer onto waterslide decal paper to enable the one-step printing of a ceramic decal is not novel (as shown for example by Banhazl). But, adding flux to that image transfer layer material is novel and expands the usefulness of the printed decal as disclosed in the present invention. The glass flux enables the creation of a ceramic decal that can be used in four-color digital ceramic laser printers such as those used in the Zimmer system, conventional monochrome (black and white) laser printers such as the H-P and Canon laser printers that use iron oxide and other inorganic materials in the black toner formulation and also for creating ceramic decals using laser printers that use machine readable MICR toner. The glass flux added to the image transfer layer material expands the variety of substrates that can be decorated to include glossy, matte, glazed and unglazed surfaces, glass and porcelain enameled surfaces. It also reduces the required firing temperature down to the range of about 1150° F.-1750° F. for low melt point glass flux. With a low lead oxide containing flux in the coated material layer, papers of this design can give the final decorations food-safe properties. The printed image transfer layer material may also be used to carry white and other color ceramic pigment as background layers in the decal, and can include a dye to differentiate one functionality from the others.
In the Zimmer ceramic printing system, this image transfer layer material is coated onto to a donor paper and applied on top of the image that was printed directly onto the waterslide decal paper. The application is performed in a secondary process step wherein the transfer film/donor paper is placed onto the printed waterslide paper and heated in a pouch laminator. This heating step releases the image transfer layer from the donor paper and attaches it to the top of the printed waterslide paper. In this format, the decal has the transfer film applied on top of the printed image. In the Zimmer system, these image transfer layers have glass flux but require this secondary processing step of lamination (or screen and aerosol application of the liquid transfer material) to produce a finished decal.
An alternative to this approach uses a waterslide decal paper that has been coated with a transfer material directly onto the waterslide decal paper (such as disclosed by Banhazl). This is then fed into the printer so that the ceramic image is printed on top of the image transfer layer. This approach has the advantage of being a one step process for the creation of a decal but none of these papers are available with flux and so their usefulness is constrained.
By using the present invention, the best features of both of these systems are captured while avoiding potential disadvantages such as: limitations on the substrates that can be decorated; requiring high firing temperatures; avoiding any effect of the obsolescence of iron oxide toner in commercial black-and-white printers like those sold by H-P and Canon; and other constraints on the nature of the decoration such as food safety.
For example, consider a ceramic artist who has been using a currently available single-step paper to transfer iron oxide images onto glossy surfaces. Assume the artist now wants to improve efficiency by firing to a much lower temperature than the temperature required by iron oxide black toner and also wants to decorate an unglazed tile that does not have a glossy surface. Also assume the artist desires to achieve a brown color instead of sepia. This is not possible with currently available one-step papers because at low temperatures there is no bonding mechanism for the iron oxide that forms the image. If fired at low temperatures onto an unglazed, non-glossy surface, the iron oxide would simply wipe off the surface. In contrast, the present invention provides a one-step printing paper with a ceramic flux added to the image transfer layer that delivers the required color and adhesion at low temperatures, as well as reducing the firing temperature thus saving energy expense.
In addition, the iron oxide toner used in many laser printers can change oxidation state during the subsequent firing process, and change from black to orange. This occurs due to the very high temperatures (1800° F.+) required to encapsulate the iron oxide pigment into the glossy surface of the decorated part. Many artists dislike this color. The present invention uses a flux with a low melting point in the release layer that significantly reduces the firing temperatures and thereby preserves a near black results to provide a much more aesthetically desirable result.